Because the picture quality is not deteriorated in the digital VTR even if editing/dubbing, etc. is repeated, industrial digital VTRs are used in, e.g., the broadcasting station. In addition, appearance of digital VTR for civil use which can be used even in general home is expected.
In the home digital VTR, the recording format having track pattern on a magnetic tape 1 as shown in FIG. 1 has been proposed.
Namely, in this recording format, video signals of one frame and four channels (hereinafter referred to as channels #1, #2, #3, #4) of speech signals (audio signals) of one frame are converted into digital signals, and those digital signals are recorded by the helical system into 10 tracks TR1, TR2, TR3, TR4, TR5, TR6, TR7, TR8, TR9, TR10. More particularly, tracking signals for correctly tracking the head, speech signals and video signals are converted into digital signals, and they are respectively recorded into tracking areas 2, speech areas 3, and video areas 4 of respective tracks. In this case, respective speech signals of the channels #1, #2 are recorded into the speech areas 3 of the track TR1.about.the track TR5 after undergone interleaving, and respective speech signals of the channels #3, #4 are recorded into the speech areas 3 of the track TR6.about.the track TR10 after undergone interleaving.
In correspondence with such a recording format, as shown in FIG. 2, reproduction heads 22a, 22b of 2 channels are oppositely provided on the outer circumference of a rotary drum 20 of the digital VTR, wherein a recording head 21b is disposed at the position rotated by 60 degrees in the counterclockwise direction with respect to the reproduction head 22a, and a recording head 21a is disposed at the position opposite to the recording head 21b. Accordingly, the recording head 21a and the reproduction head 22a are spaced therebetween in terms of angle by 120 degrees. An erase (erasing) head 23 is disposed at the position rotated by 60 degrees in the clockwise direction from the reproduction head 22a between the recording head 21a and the reproduction head 22a.
When the rotary drum 20 makes one round, video signal and speech signal of one track are recorded onto the recording tape 1 one after another by the recording heads 21a, 21b. Accordingly, when the rotary drum 20 makes five rounds, video signals and speech signals of 10 tracks in total, i.e., 1 frame are recorded onto the magnetic tape 1.
On the other hand, also at the time of reproduction, similarly to the operation at the time of recording, for a time period during which the rotary drum 20 makes five rounds, video signals and speech signals of one frame (10 tracks) are reproduced from the magnetic tape 1.
A digital VTR adapted for carrying out such a recording/reproduction includes a recording system 10 and a reproduction system 30 as shown in FIG. 3.
This recording system 10 comprises an A/D converter 13 for converting a video signal into a digital signal, A/D converters 14a, 14b, 14c, 14d for respectively converting speech signals of 4 channels into digital signals, selector (changeover) switches 15a, 15b, 15c, 15d for respectively carrying out selective switching between respective speech data from the A/D converters 14a.about.14d and respective speech data from a reproduction signal processing circuit 35 which will be described later, a recording signal processing circuit 16 for implementing a predetermined signal processing to video data from the A/D converter 13 and respective speech data selected at the selector switches 15a.about.15d, recording amplifiers 17a, 17b for amplifying a recording signal from the recording signal processing circuit 16, and recording heads 21a, 21b for recording recording signals from the recording amplifiers 17a, 17b.
More particularly, the A/D converter 13 converts a video signal delivered through a terminal 11 into a digital signal to deliver video data thus obtained to the recording signal processing circuit 16. On the other hand, the A/D converters 14a.about.14d convert respective speech signals of the channels #1.about.#4 respectively delivered through terminals 12a, 12b, 12c, 12d into digital signals to deliver speech data of respective channels thus obtained to the recording signal processing circuit 16 through the selector switches 15a.about.15d.
The recording signal processing circuit 16 implements a predetermined signal processing, e.g., encoding (modulation) based on a predetermined encoding (modulation) rule for data compression, and/or addition of error correction code for error correction at the reproduction system 30, etc. to the video data delivered from the A/D converter 13. Moreover, the recording signal processing circuit 16 implements a predetermined signal processing such as encoding, etc. to speech data of the channels #1.about.#4 respectively delivered through the selector switches 15a.about.15d. Further, the recording signal processing circuit 16 interleaves respective speech data of the channels #1, #2, and interleaves respective speech data of the channels #3, #4 so that the so-called burst error does not takes place in speech data reproduced at the reproduction system 30 to add error correction codes thereto. In addition, the recording signal processing circuit 16 carries out time-divisional multiplexing of the video data and the speech data to which the predetermined signal processing have been implemented so as to become in conformity with the above-described recording format. Namely, the recording signal processing circuit 16 carries out time-divisional multiplexing of video data and speech data so that video data of one frame are recorded into the video areas 4 of the tracks TR1.about.TR10, the interleaved speech data of the channels #1, #2 are recorded into the speech areas 3 of the tracks TR1.about.TR5, and the interleaved speech data of the channels #3, #4 are recorded into the speech areas 3 of the tracks TR6.about.TR10 to deliver a recording signal thus obtained to the recording amplifiers 17a, 17b. The recording amplifiers 17a, 17b amplify the recording signal to drive the recording heads 21a, 21b. More particularly, the recording head 21a scans, e.g., tracks TR1, TR3, TR5 . . . , and the recording head 21b scans tracks TR2, TR4, TR6 . . . to carry out recording based on the recording signals. Thus, video signals of one frame and 4 channels of speech signals of one frame are recorded into 10 tracks TR1.about.TR10 on the magnetic tape 1, as shown in the FIG. 1 mentioned above, by the recording heads 21a, 21b.
On the other hand, as shown in the FIG. 3 mentioned above, the reproduction system 30 comprises reproduction heads 22a, 22b, equalizer amplifiers 31a, 31b for respectively carrying out waveform equalization of respective reproduction signals from the reproduction heads 22a, 22b, a selector (changeover) switch 32 for carrying out selective switching between respective reproduction signals which have been waveform-equalized by the equalizer amplifiers 31a, 31b, a clock reproduction circuit 33 for reproducing a clock (clock signal) from the reproduction signal selected at the selector switch 32, an A/D converter 34 for allowing the reproduction signal selected at the selector switch 32 to be binary signal (i.e., binarizing the reproduction signal) to output reproduction data, a reproduction signal processing circuit 35 for separating video data and speech data of 4 channels from the reproduction data from the A/D converter 34, a D/A converter 36 for converting the video data from the reproduction signal processing circuit 35 into an analog signal, and D/A converters 37a, 37b, 37c, 37d for respectively converting the speech data of 4 channels from the reproduction signal processing circuit 35 into analog signals.
More particularly, the clock reproduction circuit 33 comprises a PLL circuit 33a for reproducing clock on the basis of reproduction signal selected at the selector switch 32, and a sampling clock generating circuit 33b for generating a sampling clock of the A/D converter 34 from the clock from the PLL circuit 33a.
Moreover, the reproduction heads 22a, 22b scan, one after another, tracks on the magnetic tape 1 in accordance with rotation of the rotary drum 20. Thus, the reproduction head 22a and the reproduction head 22b alternately output reproduction signals in such a manner that the former head 22a outputs reproduction signals corresponding to the tracks TR1, TR3, TR5 . . . as shown in FIG. 4A, and the latter head 22b outputs reproduction signals corresponding to the tracks TR2, TR4, TR6 . . . The equalizer amplifiers 31a, 31b carry out waveform equalization and amplification of these reproduction signals. In addition, the selector switch 32 is operative as shown in FIG. 4C to alternately select waveform-equalized reproduction signals to deliver a continuous reproduction signal to the PLL circuit 33a and the A/D converter 34.
The PLL circuit 33a generates a reproduction clock in synchronism with the clock component superimposed on the reproduction signal delivered through the selector switch 32. The sampling clock generating circuit 33b generates a sampling clock from the reproduction clock to deliver it to the A/D converter 34.
The A/D converter 34 converts reproduction signal delivered through the selector switch 32 into digital signal on the basis of the sampling clock delivered from the sampling clock generating circuit 33b so that the reproduction signal is binarized to deliver the reproduction data thus obtained to the reproduction signal processing circuit 35.
The reproduction signal processing circuit 35 decodes (demodulates) reproduction data delivered from the A/D converter 34 in correspondence with a predetermined signal processing at the recording system 10, and carries out error correction and de-interleaving to conduct separation of the video data and the speech data of 4 channels. Then, the reproduction signal processing circuit 35 delivers the video data to the D/A converter 36, and delivers the speech data of the channels #1.about.#4 to the D/A converters 37a.about.37d, respectively. The D/A converter 36 converts the video data into an analog signal to output the video signal thus obtained through a terminal 38. In addition, the D/A converters 37a.about.37d respectively convert speech data of the respective channels into analog signals to output respective speech signals thus obtained through terminals 39a, 39b, 39c, 39d.
In the above-described digital VTR, in, e.g., editing, etc., there are instances where speech signal of a certain channel is recorded in the state where it is inserted. In the above-described recording format of the digital VTR, the speech signals of the channels #1, #2 of the speech signals of 4 channels are recorded into the tracks TR1.about.TR5 after undergone interleaving, and the speech signals of the channels #3, #4 are recorded into the tracks TR6.about.TR10 after undergone interleaving. For this reason, in the case where, e.g., only the speech signal of the channel #1 is insert-recorded, the speech signal of the remaining channel #2 within the same tracks TR1.about.TR5 must be left as it is. Accordingly, the speech signal of the channel #2 reproduced by the reproduction heads 22a, 22b is sent to the recording system 10 for a second time, and is recorded into the tracks TR1.about.TR5 after it is interleaved with a speech signal of the channel #1 delivered through the terminal 12a.
In more practical sense, the speech signal of the channel #1 delivered through the terminal 12a is converted into speech data at the A/D converter 14a to set the selector switches 15a, 15b so that the selector switch 15a selects speech data from the A/D converter 14a and the selector switch 15b selects the reproduced speech data of the channel #2 from the reproduction signal processing circuit 35. In addition, the recording signal processing circuit 16 interleaves new speech data of the channel #1 selected by the selector switch 15a and the speech data of the channel #2 selected by the selector switch 15b, and implements a predetermined signal processing such as addition of error correction code, etc. to generate a recording signal with respect to the speech areas 3 of the tracks TR1.about.TR5 to deliver this recording signal to the recording heads 21a, 21b through the recording amplifiers 17a, 17b.
Here, as shown in the FIG. 2 mentioned above, since rotation angles of the recording heads 21a, 21b are delayed (shifted) by 120 degrees with respect to the reproduction heads 22a, 22b, the recording signal delivered to the recording heads 21a, 21b is delayed by the time corresponding to 120 degrees in terms of the rotation angle of the rotary drum 20 with respect to the reproduction signal from the reproduction heads 22a, 22b as shown in FIGS. 4E, 4F. Moreover, at this time, as shown in FIG. 4D, erase current is delivered to the erase head 23 in a manner preceding by the time corresponding to 60 degrees in terms of the rotation angle of the rotary drum 20 with respect to (supply of) recording signal to the recording head 21a. Thus, the speech signal of the channel #1 is insert-recorded into the tracks TR1.about.TR5. It is to be noted that, in practice, reproduction signal reproduced by the reproduction heads 22a, 22b from the magnetic tape 1 is delayed by, e.g., about (1+1/3) frames by the reproduction signal processing circuit 35, etc., and is further delayed by about (1+1/3) frames by the recording signal processing circuit 16, whereby the reproduction signal is recorded onto the magnetic tape 1 in the state delayed by about (2+2/3) frames in total. In addition, since the speech signals of the channels #3, #4 are only reproduced, setting of the selector switches 15c, 15d has not relevancy to the above-described operation. In this example, however, those switches are assumed to be switched so as to select speech data from the reproduction signal processing circuit 35.
Meanwhile, the level of the reproduction signal outputted from the reproduction heads 22a, 22b is 1/1000.about.10000 of recording signal delivered to the recording heads 21a, 21b or erase current delivered to the erase head 23. The crosstalk of the recording signal or erase current with respect to the reproduction signal becomes problem. Namely, in the case where video signals and speech signals are simply recorded, or video signals and speech signals are simply reproduced, there is no problem. However, in the case where speech signal of a certain channel is insert-recorded as described above, since erasing or recording operation is carried out when the reproduction heads 22a, 22b are scanning the speech areas 3, the recording signal (designated at B, C in FIG. 4) or erase current (designated at A in FIG. 4) leaks into reproduction signal of speech signal, leading to deterioration of the signal-to-noise ratio (so called S/N ratio) of the reproduction signal. As a result, error rate is lowered. Further, in the case where crosstalk is large, it becomes impossible to correctly reproduce the video signal and/or the speech signal from the magnetic tape 1. In other words, in the conventional digital VTR, in the worst case, the speech signal of the channel #1 would be unable to be insert-recorded in the state where, e.g., the speech signal of the channel #2 is held on the magnetic tape 1.
This invention has been made in view of actual circumstances as described above, and its object is to provide a recording and reproduction apparatus in which, in insert-recording a speech signal of a certain channel, a measure can be taken such that the crosstalk of a recording signal of a channel which is to be insert-recorded does not affect reproduction signal of speech signal of channels recorded as they are.